The PySide.QtGui.QPainter class performs low-level painting on widgets and other paint devices. The QPainter class provides all the functions to draw simple lines to more complex shapes. This class also provides settings to render quality images and supports clipping. The drawing is usually done within the widget's paintEvent() function. The drawing functionalities are placed in between the begin() and end() functions of the QPainter object. The QPainter object is initialized with the constructor, customized with some set functions, such as pen style and brush style, and then the draw function is called. The QPainter.isActive() function indicates whether the painter is active. The QPainter object is activated when QPainter.begin() is invoked and deactivated on calling QPainter.end().

The various drawings are performed using the QPainter's draw functions. The QPainter has three important settings that set the appearance of the drawing. They are as follows:

The settings for these parameters can be set and modified anytime by calling the setFont(), setBrush(), and setFont() on QPainter with their respective QPen, QBrush, or QFont objects.

In this section, we are going to explore the most commonly used drawing shapes. The following table will give you a gist of the available draw functions of the QPainter object:

All the earlier-listed functions take various arguments as their parameters for different drawing functionalities. Also, all these drawing functions use the current pen, brush, and text settings to draw the objects. This section is not enough to cover and discuss all the different types of drawing functions, and hence, we should look at a sample program that is self-explanatory and exhibits the different styles of the listed functions. The complete version of the basic drawing functionality code can be downloaded from this book's site. Here, we just display the contents of the paintEvent() function with different drawing shapes. The complete code is bundled with event handling that we have discussed in the first section of this chapter and the usage of other built-in widgets, such as combobox, that we will discuss in the next chapter. As of now, it is sufficient if you can understand the reimplementation of the event handlers and drawing functions of the program:

def paintEvent(self, event):
    rect = QRect(10, 20, 80, 60)

    startAngle = 30 * 16
    arcLength = 120 * 16

    painter = QPainter()
    painter.begin(self)
    painter.setPen(self.pen)
    painter.setBrush(self.brush)
    if self.shape == PaintArea.Line:
      painter.drawLine(rect.bottomLeft(), rect.topRight())
    elif self.shape == PaintArea.Points:
      painter.drawPoints(PaintArea.points)
    elif self.shape == PaintArea.Polyline:
      painter.drawPolyline(PaintArea.points)
    elif self.shape == PaintArea.Polygon:
      painter.drawPolygon(PaintArea.points)
    elif self.shape == PaintArea.Rect:
      painter.drawRect(rect)
    elif self.shape == PaintArea.RoundRect:
      painter.drawRoundRect(rect)
    elif self.shape == PaintArea.Ellipse:
      painter.drawEllipse(rect)
    elif self.shape == PaintArea.Arc:
      painter.drawArc(rect, startAngle, arcLength)
    elif self.shape == PaintArea.Chord:
      painter.drawChord(rect, startAngle, arcLength)
    elif self.shape == PaintArea.Pie:
      painter.drawPie(rect, startAngle, arcLength)
    elif self.shape == PaintArea.Path:
      painter.drawPath(path)
    elif self.shape == PaintArea.Text:
      painter.drawText(rect, QtCore.Qt.AlignCenter, "Basic Drawing Widget")
    painter.end()

This will produce a window, as displayed in the following screenshot. You can select the choice of your drawing from the comboboxes, and it will be painted in the application.